Elevated pressure product, such as oxygen and nitrogen, produced by the cryogenic rectification of feed air is increasing in demand due to such applications as coal gasification combined-cycle power plants where all of the products from the cryogenic rectification plant may be used at the elevated pressure.
One way of Producing elevated pressure product from a cryogenic rectification plant is to compress the products produced by the plant to the requisite pressure. However, this approach is costly both because of the initial capital costs and because of the high operating and maintenance costs for the compressors.
Another way of producing elevated pressure product from a cryogenic rectification plant is to operate the plant columns at a higher pressure. However, this puts a separation burden and thus a recovery burden on the system because cryogenic rectification depends on the relative volatilities of the components and these relative volatilities are reduced with increasing pressure. This is particularly the case where liquid oxygen and/or liquid nitrogen products are desired from the cryogenic rectification plant as this reduces the availability of high quality reflux which may be used to improve the separation and thus increase the Product recovery at higher rectification pressures.
Accordingly, it is an object of this invention to provide a cryogenic rectification system which can produce product at elevated pressure with improved recovery over that attainable with conventional systems.